1. Field of the Invention
The present invention relates to an apparatus for manufacturing tyres, and to a method of manufacturing tyres put into practice by said apparatus.
2. Description of the Related Art
The main constituent elements of a tyre generally comprise a carcass structure including at least one carcass ply having end flaps engaged with respective annular anchoring structures, said anchoring structures being each usually formed of a substantially circumferential annular insert currently referred to as bead core, to which, at a radially external position, at least one filling insert is applied.
Associated with the carcass structure is a belt structure comprising one or more belt layers, disposed in radial superposition with respect to each other and to the carcass ply and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. Applied to the belt structure at a radially external position is a tread band of elastomer material in which a raised pattern for tyre contact with the ground is formed.
It is to be pointed out, to the aims of the present description that by the term “elastomer material” it is intended a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably this composition further comprises additives such as a cross-linking agent and/or a plasticizer. Due to the presence of the cross-linking agent, this material can be cross-linked through heating, so as to form the final article of manufacture. In addition, respective sidewalls of elastomer material are applied to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads.
The carcass structure and belt structure, together with the respective tread band, can be made separately from each other in respective work stations, to be mutually assembled at a later time.
According to conventional manufacturing methods, the tread band and sidewalls are made each from a continuously extruded section member that, after cooling for stabilising its geometrical conformation, is stored on suitable tables or reels. The semifinished product in the form of sections or a continuous strip is then sent to a feeding unit the task of which is to pick up the sections or cut the continuous strip into sections of predetermined length, each of them constituting the tread band or one of the sidewalls to be circumferentially applied to the tyre under working.
As described in document U.S. Pat. No. 3,380,872, the carcass plies and annular anchoring structures of a tyre are assembled on a reference support comprising a membrane having circumferential edges in engagement with respective opposite circular flanges keeping the membrane taut in a cylindrical conformation. When assembling of the carcass structure is completed, compressed air is admitted into the membrane to radially expand it and give it a toroidal conformation. Should the conformation be insufficient, the opposite flanges can be mutually approached. The other constituent elements of the tyre, such as the belt structure, tread band and sidewalls, can be applied to the carcass structure thus formed. The manufactured tyre is then removed from the reference support to be subsequently vulcanised.
Document U.S. Pat. No. 5,853,526 discloses formation of the green tyre through assembly of its constituent elements using an inflatable bladder as the reference support, said bladder being inflated to a predetermined pressure and being subsequently introduced into a vulcanisation mould together with the green tyre formed on said support.
In accordance with documents U.S. Pat. No. 6,318,432, U.S. Pat. No. 6,635,132 and US 2002-029841 in the name of the same Applicant, each constituent element of the tyre is formed through direct application on a toroidal rigid building support of one or more elementary components such as elongated elements or strips of elastomer material, rubberised metallic or textile cords, strip-like elements of rubberised cords, or others, so as to enable manufacture of tyres without requiring that a plurality of semifinished products be manufactured and stored.